This invention relates to a method and apparatus for providing a compressed air charge, i.e. boost pressure, to an internal combustion engine by an air compressor called a supercharger and by a turbocharger which includes another air compressor driven by a turbine driven by exhaust gases from the engine.
The present invention is directed to the effective combination of a supercharger and turbocharger with an internal combustion engine to provide a power system for a vehicle or the like with reasonably competitive fuel efficiency, horsepower and torque. While the present invention is not limited to use only in vehicles, it will be described in connection therewith as that is its preferred useage. In some vehicles, a supercharger (which is driven directly by the engine) is used to provide boost pressure without the use of a turbocharger. In other vehicles, only a turbocharger is used for the reason that it is not directly driven by the engine and therefor significantly reduces the fuel consumption of the engine when compared to a supercharger.
The present invention is particularly directed to the elimination of the so-called "turbo lag" which results from the fact that the turbocharger does not provide sufficient of boost pressure until the automotive engine has speeded up to several thousand revolutions per minute; and this means a few seconds in delay i.e., a lag in achieving the extra torque to accelerate the vehicle quickly. Thus, when the turbocharged vehicle is being called upon for rapid acceleration, as is typical for an automotive vehicle to move from a dead stop, the extra torque needed is not available. A conventional automotive vehicle needs sufficient torque to bring it rapidly to driving speed and the driver will not tolerate a few seconds wait for the turbo lag to be overcome by the turbocharger, if the turbocharger is to provide the extra torque for a fast start.
The combination of both a supercharger and a turbocharger to provide boost to an engine has been heretofore proposed, as for example, in Buchi Pat. No. 2,296,268. This patent discloses a centrifugal supercharger which is continuously driven and supplying boost pressure first to the engine manifold directly through one pipe. Then when the turbo charger is delivering more boost pressure to the engine than the supercharger, the excess pressure forces a vaned damper to close and redirect the flow of the supercharger into and through the turbocharger. In the centrifugal compressor, air will recirculate within the centrifugal compressor and cause a significant load that will decrease the efficiency of the system even when the damper valve is closed in the air conduit between the supercharger and the turbocharger. The supercharger uses considerable power at high engine speeds.
Kitchen U.S. Pat. No. 3,335,563 discloses a turbocharger which delivers a compressed air charge through the supercharger to the intake manifold of the vehicle engine. Both U.S. Pat. Nos. 2,296,268 and 3,335,563 disclose relatively inefficient systems in that the supercharger operates continuously; and, at higher engine speeds will consume considerable horsepower. Such use of horsepower detracts significantly from the fuel efficiency.
A further discussion of the use of a combination of a turbocharger and supercharger with an internal combustion engine is disclosed in McInerney, et al., U.S. Pat. No. 3,921,403 in which a supercharger is used to supply boost pressure when the engine throttle is rapidly opened to reduce the amount of exhaust smoke emanating from the engine during acceleration. In this particular patent, the engine directly drives a fluid pump which in turn drives a fluid motor connected to the supercharger. The fluid pump and fluid motor are constantly driven, and hence, use considerable horsepower at higher engine speeds. This patent discloses a further embodiment with a continuously driven fluid pump, which drives the fluid motor to turn the supercharger until the turbocharger operates sufficiently and then the pump drives a fluid motor operating a fan for circulating air about an after-cooler. Again, while the burst or puff of smoke may be eliminated during acceleration, fuel efficiency is lacking because of the continuous and direct drive of the fluid pump and the fluid motors directly by the engine at all engine speeds. The use of fluid pumps and fluid motors results in increased expense and size for the system making the system unsuitable for automotive use. Further, each of the fluid pumps and fluid motors have its own inefficiency to make the overall system less efficient than a simple direct drive belt or the like. The diesel engine disclosed in U.S. Pat. No. 3,921,403 also appears to be used for a relatively narrow range of speeds in an industrial appplication because its turbocharger does not appear to have a wastegate valve which is used with turbochargers for the widely varying loads and speeds such as encountered in automotive use.
The present invention is particularly directed to providing a supercharged and turbocharged system for use with a vehicle engine so that a small internal combustion engine may act as a larger engine of increased horsepower during rapid acceleration, but which is also able to achieve the economy of fuel conservation by use of the turbocharger alone at higher engine speeds. Unlike industrial diesel applications in which the supercharged or turbocharged engine is only for a specific narrow speed and/or load range, the present invention is useable with the widely varying speed and load conditions encountered with vehicle propulsion. To be commercially feasible, the system should have the supercharger and turbocharger interrelated to each other and to the engine to achieve fuel economy while providing the increased horsepower and torque from the boost pressure provided to the engine. For conventional automobiles used for general public useage, to which the present invention is primarily directed, the cost of the system should be low in contrast to race vehicles where exotic and costly systems have heretofore been used.
Accordingly, a general object of the present invention is to provide a new and improved internal combustion engine system employing a supercharger and turbocharger.
Another object of the invention is to provide a new and improved supercharger and turbocharger system for use with internal combustion engines used to power conventional, mass produced automobiles and trucks.